French forces in northern Mali have killed a senior commander of the al Mourabitoun Islamist group who was wanted by the United States, a defense ministry spokesman said on Thursday.

The United States has offered a $5 million reward for information leading to the arrest of Ahmed al Tilemsi, who took part in the 2011 kidnapping of two French nationals in Niger and of three aid workers in Algeria later that year.

Al Tilemsi was a founding member of the Movement for Unity and Jihad in West Africa (MUJWA), which merged with fighters loyal to veteran Islamist leader Mokhtar Belmokhtar to form al Mourabitoun last year.

“Last night, we launched an operation in the Gao region in coordination with Malian forces,” Colonel Gilles Jarron told reporters in Paris. He added that Tilesmi had been killed and a dozen other Islamists 'neutralized', but did not specify if that meant killed or arrested.

MUJWA, Belmokhtar's men and members of al-Qaida's north Africa arm, AQIM, formed a loose alliance of fighters that seized northern Mali's desert regions in 2012.

The militants were scattered by a French offensive in January 2013 but France has kept about 3,200 troops in the Sahara-Sahel region as part of a counter-insurgency force.

An additional 200-400 special forces have a mandate to hunt down leaders of the Islamist groups, which have mounted a resurgence in recent months with a series of attacks that have killed dozens of U.N. peacekeepers in Mali.

The last of the French hostages held by the al-Qaida-linked militants was freed earlier this week. However, sources said Mali released at least two Islamists in return, angering local rights groups.